I always thought the implication was that they WERE demons, and the press calling them aliens was just them misunderstanding. After all, the news reports said they were being beaten by, irrc, "traditional" methods, not water. Wouldn't they have just said water if that was it? I think we are meant to ultimately infer that some of them were beaten by different holy tricks, like prayer scrolls in come parts of the word, incense in others, and the water of a holy man in the case of the main characters.
Split was pretty good for what it was. Was Unbreakable terrible? I rewatched the Sixth Sense recently, it wasn't terrible but I think people are a bit too lenient with it because at the time it came out it was very much an 'event' - like, back when going to see films in a theatre was a thing (then waiting a year or so for it to come out on home video), the fact that there was a 'twist' kind of mattered more, so there was word of mouth and buzz about talking about the twist or people seeing it because it was eventful. But it doesn't really have a lot going for it in terms of rewatchability.
And, I haven't seen the fault in our stars but I BET IT IS PRESTIIIIIIIIIIIIIIIGGGGEEEEEEEEEEEE
(Sorry, I just find that really funny for some reason)